41 C.F.R. § 301-51.101
Cash-equivalent payment methods
(a) The following payment methods are considered the equivalent of cash:
(1) Personal credit cards;
(2) Cash withdrawals obtained from an ATM using a Government contractor-issued individually billed travel charge card; and
(3) Checks, both personal and travelers.
(b) Agencies must comply with § 102-118.30 of this title, which limits payment of transportation services to electronic fund transfer (EFT), unless excepted.